In-situ investigations of the amorphous-to-crystalline transformation of ITO films by synchrotron X-ray scattering

Amorphous tin-doped indium oxide (ITO) films were grown by reactive pulsed middle frequency dual magnetron sputtering on Si (100) substrates covered with 500 nm SiO2. Changes in the microstructure and the resistivity of the ITO films during annealing in vacuum (p ~ 10-6 mbar) were characterized by in-situ synchrotron XRD analysis and simultaneous four-point probe measurements at ROssendorf Beam Line (ROBL). The in-situ experiments are performed at isothermal (temperature range of 210 - 240 °C) and non-isothermal (T-ramp: 2.5 - 10 K/min) annealing modes.
At non-isothermal annealing the XRD data reveal a rapid crystallization in the temperature range of 240 - 280°C. The heating rate does not influence on the temperature of the crystallization onset (T=240 ± 10 °C).
At isothermal annealing increase of the temperature leads to decrease of the time of crystallization onset and the total time of amorphous-to-crystalline transformation and, therefore the crystallization rate increases. Using the Kolmogorov-Avrami-Johnson-Mehl equation [f ~ 1-exp(-ktn)] for the dependence of the crystalline fraction f on the annealing time, the kinetic parameters of crystallization were determined. On the condition that the coherently diffracting domain size (~65 nm) is smaller than the film thickness (~130 nm) a three-dimensional crystallization process was indicated.
Even in amorphous films the resistivity significantly decreases with increasing temperature, likely by the generation of oxygen vacancies. The rapid crystallization leads to further reduction of the resistivity probably due to Sn donor activation.